This invention is directed to implants used in spinal fixation surgery and more particularly is directed to means for anchoring artificial ligament tape in a construct for tethering an uppermost fused vertebra to higher vertebrae.
The prior art discloses a variety of structures and methods for treating one or more degenerated, deformed or damaged vertebral stages of a patient's spinal column by means of internal spinal fixation. Typically, this involves the attachment of a spinal implant system to provide a construct that is attached to two or more adjacent vertebrae to support and stabilize the vertebrae in order to allow them to fuse together in a stationary relationship relative to each other. Spinal fusion constructs typically include pedicle screws and longitudinal support members or rods that are attached to the pedicle screws and together they fix the position of the adjacent vertebrae to which they are attached.
However, a problem that develops after surgery in many patients as a result of patient activity or stature is that the vertebra that is immediately above the highest fused vertebra breaks away from the highest fused vertebra and falls forward. Surgeons sometimes attempt to prevent that problem by securing vertebrae that are immediately above the uppermost instrumented vertebra to the uppermost instrumented vertebra by means of artificial ligament tape. (An instrumented vertebra is a vertebra to which a device is implanted or connected.)
One way of doing this is to first drill a hole through the spinous process of the uppermost instrumented vertebra and also the contiguous vertebrae that are immediately above the uppermost instrumented vertebra and are to be secured by the ligament tape. The ligament tape is then threaded through the drilled holes upward from the uppermost instrumented vertebra to the higher vertebrae and then threaded back down again through the holes to the uppermost instrumented vertebra. In one procedure the ligament tape is then pulled in tension and tied to itself or to one or two of the rods that are a part of the construct. Unfortunately, this procedure often results in a loosening of the ligament tape because much of the tension is lost during the manipulation of the ligament tape into a knot and also because the tape can loosen further after surgery from slippage of the knot.
In order to reduce this loosening problem, the prior art has provided specialized anchoring devices that are attached to the construct and allow the surgeon to fasten the ligament tape to the construct. These specialized anchoring devices avoid the use of a knot and also allow a greater tension to be maintained while the tape is being secured to the anchors and thereby reduce or eliminate later slippage at the anchor. However, these specialized anchoring devices result in a construct that adds them as one or more additional devices that must be included in the construct. The additional devices increase the space occupied by the construct, require additional manipulation by the surgeon, must be taken into account when closing the wound and increase cost.
It is therefore an object and feature of the invention to provide a structure for anchoring the artificial ligament tape without requiring the surgeon to mount any additional specialized anchoring devices on the support rods or any other part of the construct.
The term “artificial ligament tape” is used in a generic sense to refer to a type of cordage that is available for surgeons to perform the procedures that are described above. Some prior art refers to equivalent structures as tape, cable, rope, tether, wire, braid, band or strand. They are an elongated structure that is flexible so that they bend easily (with the application of relatively little force) but also have a strong resistance to being stretched longitudinally by a substantial pulling force. Other equivalent terms include artificial ligament reconstruction tape, Mersilene tape and TLS® strips.